This invention relates to microelectromechanical systems and/or nanoelectromechanical systems (collectively hereinafter “microelectromechanical systems”) and techniques for fabricating microelectromechanical systems; and more particularly, in one aspect, for fabricating or manufacturing microelectromechanical systems having mechanical structures that are encapsulated using thin film or wafer level encapsulation techniques in a chamber, and including an integrated getter area and/or an enhanced volume of the chamber.
Microelectromechanical systems (“MEMS”), for example, gyroscopes, resonators and accelerometers, utilize micromachining techniques (i.e., lithographic and other precision fabrication techniques) to reduce mechanical components to a scale that is generally comparable to microelectronics. MEMS typically include a mechanical structure fabricated from or on, for example, a silicon substrate using micromachining techniques. For example, with reference to FIG. 1A, a MEMS resonator typically includes mechanical structure 12, including movable electrode 14, fixed electrodes 16a, 16b and 18, anchors 20a and 20b, and periphery area 22 that surrounds and/or borders mechanical structure 12.
Notably, in conventional MEMS, the fixed electrodes and the periphery area tend to be solid or contiguous structures (see, for example, fixed electrode 16a and periphery area 22 in FIGS. 1A and 1B). In this regard, the mechanical structure is typically fabricated from or on, for example, a silicon substrate. The silicon substrate is disposed on an insulation layer that, among other things, serves as a sacrificial layer for the MEMS. During fabrication, the movable and fixed electrode electrodes, anchors 20a and 20b, and periphery area 22 are formed and significant portions of the insulation layer are etched or removed in order to release the moveable electrodes of the mechanical structure. (See, for example, U.S. Pat. Nos. 6,450,029 and 6,240,782). In this way, the mechanical structure may function, for example, as a resonator, accelerometer, gyroscope or other transducer (for example, pressure sensor, strain sensor, tactile sensor, magnetic sensor and/or temperature sensor). Notably, the fixed electrodes and the periphery area are solid and/or contiguous structures that are largely unaffected during the release of the moveable electrodes.
After fabrication of the mechanical structures, those structures are typically sealed in a chamber. Conventional MEMS seal these structures in, for example, a hermetically sealed metal or ceramic package. Conventional MEMS also employ bonding encapsulation techniques whereby a semiconductor or glass-like substrate having a chamber to house, accommodate or cover the mechanical structure is bonded (for example, via anodic, frit glass or fusion bonding) to the substrate in which the mechanical structures are formed (see, for example, U.S. Pat. Nos. 6,146,917; 6,352,935; 6,477,901; and 6,507,082).
Such conventional MEMS typically provide a relatively large volume and often include a getter material to “capture” impurities, atoms and/or molecules that are out-gassed from, for example, the silicon substrate, during operation. As such, conventional MEMS exhibit a relatively stable pressure within the chamber over a significant period of time and operating conditions (for example, operating over a large range of operating temperatures which tend to induce release of impurities, atoms and/or molecules).
Another encapsulation technique employs a thin film approach using micromachining during, for example, wafer level packaging of the mechanical structures. (See, for example, International Published Patent Applications Nos. WO 01/77008 A1 and WO 01/77009 A1). Conventional MEMS having mechanical structures that are packaged at the wafer stage tend to have a smaller volume relative to hermetically ceramic packages and bonding encapsulation techniques. In addition, due to subsequent processing (often at high temperatures), thin film wafer level packaged MEMS are not able to effectively employ a getter material to “capture” impurities, atoms and/or molecules that are out-gassed from surrounding materials. As such, conventional thin film wafer level packaged MEMS are more susceptible to pressure instability within the chamber. This instability may increase over time and operating conditions (for example, operating over a large range of operating temperatures).
Thus, there is a need for, among other things, a MEMS employing thin film wafer level packaging techniques that overcomes one, some or all of the shortcomings pertaining to gettering and volume constraints of the conventional thin film wafer level packaging techniques. There is a need for, among other things, a MEMS, including mechanical structures that are encapsulated using thin film encapsulation, that includes enhanced getter capabilities and/or an enhanced volume of the chamber containing the mechanical structures with little to no increase in overall dimensions of the MEMS. In this way, the thin film wafer level packaged MEMS of the present invention includes a relatively stable, controlled pressure environment within the chamber to provide, for example, a more stable predetermined, desired and/or selected mechanical damping of the mechanical structure(s).